When an image is captured by a digital camera, noise may be added depending on the characteristics of the CCD (Charge-Coupled Device) or the CMOS read-out circuit or the characteristics of the transfer path. There are also out-of-focus image blur which occurs when the object is not in focus when capturing an image thereof, and image blur which occurs due to camera shake, or the like. Thus, captured images have noise due to characteristics inherent to captured images, as well as blur caused by human operations during the picture-taking operation, thereby deteriorating the images. Of these types of “blur”, image blur due to camera movements during picture-taking (exposure) will be referred to as “motion blur”, distinguished from out-of-focus blur.
In recent years, as demands for high-sensitivity photography are particularly increased, it is necessary to restore an image which has deteriorated due to blur (hereinafter referred to as a “deteriorated image”) to an image that is as close as possible to an original image (hereinafter referred to as an “ideal image”. In order to realize a bright image without noise or blur which is required for high-sensitivity photography, there are generally two approaches, i.e., to increase the sensitivity and to elongate the exposure time.
However, increasing the sensitivity also amplifies noise, and the signal is buried under noise, often resulting in an image mostly covered by noise. On the other hand, by elongating the exposure time, it is possible to accumulate more of light present in the scene, thereby obtaining an image with little noise. In this case, the signal is not buried under noise, but the image may have motion blur due to camera shake.
In view of this, countermeasures are taken conventionally by two approaches in cases in which the exposure time is elongated. One is optical camera shake correction such as lens shift or sensor shift. The other is a method (a restoration method by signal processing) of obtaining the direction/magnitude of motion blur from an obtained image so as to restore the image by signal processing from the direction/magnitude of motion blur. Restoration methods by signal processing are disclosed in, for example, Patent Document No. 1, Patent Document No. 2, and Non-Patent Documents Nos. 1-5.